The invention relates to a process for introducing a fluid into a cavity or a blood vessel of a human or animal body, particularly for gas insufflation in preparation for or during a minimally invasive surgical procedure or investigation of the body cavity or blood vessel and an apparatus for performing the process.
In endoscopic interventions in human or animal bodies, for example in the abdominal region (in laparoscopy), the uterus (in hysteroscopy) or the joints (in arthroscopy) it is necessary to expand the cavity by means of a gas, for which carbon dioxide is preferably used. The space thus produced gives a sufficiently large operating and observation area enabling the operator to carry out the necessary medical interventions through suitable means of access to the body cavity.
During an operation or investigation a substantially constant internal pressure must be maintained in the body cavity since pressure fluctuations cause movements in the walls of the body cavity which can considerably disrupt the surgeons work or even make it impossible.
In order to maintain a constant pressure when introducing a gas into a part of the body which is to be treated medically, various pressure regulating circuits have been proposed which differ substantially in the nature and method of measurement and the place where the pressure measurement is carried out.
German patent 36 11 018 proposes an apparatus for insufflating gas, which has an insufflation instrument attached to a gas supply line. In the gas supply line are a pressure reducer, a flow meter and a pressure sensor arranged in series.
A control circuit switches the pressure reducer, as a function of a timer, in order to vary the working pressure in the gas supply line. The apparatus thus works intermittently in insufflation phases and measuring phases, whilst in the latter the supply of gas into the body cavity is reduced or interrupted and the intra-abdominal (static) pressure can then be measured substantially by means of the pressure sensor. Depending on the measurement obtained the electronic control circuit will automatically decide whether insufflation is to be continued with an increased insufflation pressure or--once the desired level of internal pressure is reached--the apparatus is subsequently operated at a reduced insufflation pressure in a so-called maintaining mode.
The solution described above has the serious disadvantage that the actual insufflation process is frequently interrupted in order to carry out the measurements until the desired internal pressure is reached. The need for regular monitoring of a constant pressure also requires further measuring phases even after the nominal pressure has been reached.
However, each interruption in the insufflation of gas will lead to a detrimental pulsing in the hollow organ in question which will interfere with the surgical procedure to a greater or lesser extent. In addition, the constant interruption to the supply of gas, particularly during the initial phase of insufflation, leads to a considerable reduction in the quantity of gas insufflated, with the result that the gas throughput per unit of time (gas flow) required for certain applications cannot be achieved and even in less demanding applications a long insufflation period is needed before the nominal pressure is achieved. A delay of this kind may be a considerable operating risk in certain cases.
Furthermore, it is known from German Utility Model 75 08 556 to carry out the introduction of gas into a body cavity and measurement of the corresponding intra-abdominal pressure through various means of access to the body cavity in order to be able to carry out pressure measurement and the introduction of gas simultaneously. This solution has the disadvantage that another incision has to be made into the body cavity for the measuring sensor. This is an additional burden on the patient and may in some cases lead to an uncontrolled escape of gas. Furthermore, because the access for the measuring sensor occasionally lead into the fatty tissue or an adjacent part of the body cavity to that where the insufflation is being carried out, there is the risk of mismeasurement with all its consequences.
DE-OS 34 13 631 describes an apparatus for non-intermittent insufflation of a gas. It has, inter alia, a measuring device for measuring the speed of the gas flow and a measuring device for measuring the pressure in the gas supply line used for the insufflation. The flow resistance of the insufflation line is determined by means of the speed of the gas flow and the actual intra-abdominal pressure is calculated therefrom, taking into account the constantly measured tube pressure, in an electronic evaluation circuit. However, this solution has two serious disadvantages:
On the one hand, the resistance level of the insufflation line is determined only once, ie. at the start of insufflation. This means that any change in the characteristics of the insufflation system, e.g. a change of insufflation instrument, is not taken into account. On the other hand, when measuring the intra-abdominal pressure, there is a presupposition that there is a linear correlation between the drop in pressure through the insufflation line and the corresponding flow quantity (gas flow). However, this linearity occurs fundamentally only in a limited range of gas flow values and is only approximate. With a higher gas throughput, in particular, this precondition does not apply, as has been confirmed by experimental tests, and in the process described above, erroneous results would be obtained for the internal pressure of the body cavity or organ.
The erroneous values obtained under the false assumption of a linear correlation between the fall in pressure and gas flow for the intra-abdominal pressure in insufflation results in a substantial risk of injury to the patient, particularly when a fairly large quantity of gas is being insufflated per unit of time. This danger consists in particular in over-extension of the insufflated organ, cavity or blood vessel, which might in some cases be irreversible.
The use of the methods described above are generally subject to strict limits, with the present degree of progress of minimally invasive medicine, as a result of the fact that shorter and shorter treatment times and higher insufflation rates are required whilst maintaining a very constant pressure level, the latter presupposing an exact and virtually continuous measurement of the internal body pressure.